Machines which process flat articles, such as paper, envelopes, tape and film, are well known in the art. Although the machines take on a wide variety of configurations depending upon the particular functions which they are designed to perform, they all share some common features. Typically, the machines include a transport system for transporting the article along a feed path through the machine. The transport system usually consists of a belt, roller or O-ring drive system and pressure rollers which work cooperatively to feed the article. Pressure rollers are disposed above the drive system so that the article passes between the nip of the drive system and pressure rollers during feeding. Generally, the pressure rollers are spring biased toward the drive system. In this manner, the pressure rollers prevent slippage of the article during feeding by keeping the article in physical contact with the drive system. A few examples of machines employing drive systems with associated pressure rollers are: postage meters, mailing machines, inserters and photographic film processing apparatus.
Article processing machines often require the transport system to have the capability to automatically accommodate various thicknesses of flat articles. This allows the machines to process a variety of articles having different sizes and configurations without the need for operator intervention. Thus, it is known in the prior art to have pressure rollers that deflect away from the drive system in proportion to the thickness of the article as the article passes through the nip and then return to a home position after the article leaves the nip.
Many different approaches are known which achieve this result. A first approach is to rotatively mount the pressure roller to one end of an arm using a shaft while pivotally mounting the other end of the arm in a location that does not interfere with the feed path of the article. A spring is then operatively coupled to the arm so as to bias the pressure roller against the drive system. Thus, when the article enters the feed nip, the arm pivots and lifts the roller away from the drive system. Accordingly, the spring bias keeps the pressure roller in contact with the article and returns the pressure roller into contact with the drive system after the article leaves the feed nip. A second approach is to rotatively mount the pressure roller to an extended shaft and rotatively mount the ends of the shaft to bearing blocks. The bearing blocks are then slideably mounted in slots located in any suitable fixed structure. Analogous to that of the first approach, the bearing blocks are spring loaded so that the pressure roller is biased toward the drive system.
Although these prior art approaches generally work well, they suffer from certain drawbacks. First, the springs must be particularly adapted to the thickness and weight of the article as well as the speed with which the article is being fed. If the spring rate is too small, then the pressure roller may bounce (deflect too much too fast) due to the impact of the article and provide insufficient force on the article to maintain it in contact with the drive system. If the spring rate is too large, then the pressure roller may drag (not deflect enough) and provide excessive force on the article. Both of the conditions are undesirable because jams and the destruction of the article are likely to result. Thus, manual adjustments to the pressure roller assembly are often necessary depending upon the configuration of the article. Second, these systems are not well adapted to accommodate off center loading. If only a portion of the pressure roller is in contact with the article, then one end of the roller tends to deflect more than the other end of the roller. Off center loading also occurs when stepped mail is processed by envelope handling apparatus. Stepped mail does not have uniform thickness across its width (the direction transverse to the path of travel) due to the contents located inside the envelope. In these situations, the bearing blocks tend to bind because they are not deflecting uniformly. As a result, uneven pressure is supplied to the article and jams and the destruction of the article are again likely.
Accordingly, there is a need for a pressure roller assembly that accommodates a wide variety of articles having different thicknesses without the need for manual adjustment. Additionally, there is also a need for a pressure roller assembly that accommodates off center loading without binding and which supplies more uniform pressure to the article.